Loud-speaker assembly



Oct. 1, 1963 c. R. EVANS LOUD-SPEAKER ASSEMBLY Filed May 16, 1961 my 6mmW %m M m M W 0 W m m United States Patent 3,105,569 LOUD-SPEAKERASSEMBLY Chauncey Richard Evans, Salt Lake City, Utah, assignor to AtuhCorporation, Salt Lake City, Utah, a corporation of Utah Filed May 16,1961, Ser. No. 110,465 3 Claims. (Cl. 181-31) This invention relates toa method of and apparatus for improving the quality of music emittedfrom a loudspeaker enclosure.

in recent years, there has been much interest in high fidelity systemsfor the reproduction of recorded music. Also, there has been acontinuing demand for high quality electrical systems for use withmusical instruments such as guitars. For the most part, designers ofelectrical sound systems have concentrated their efforts on the faithfultranslation of signals into sound without material alterations inquality.

However, some workers in the field have recognized that accuratereproduction of the input signals need not be the goal of a design ofsuch a system. The real objective is the production of music that issatisfying to the human ear, and it has been found that the overallquality of the music may be improved by judiciously emphasizingparticularly desirable components and :deernphasizing components thattend to be unpleasant.

One component that may be de-emphasized to good advantage has afrequency of around 3,000 c.p.s. For example, the finger noisesgenerated in playing a guitar frequently fall in this frequency range.

An electric circuit for minimizing components in the 3,000 cps. range isdisclosed in the prior application of Evans and Fowler, Serial No.854,777, filed November 23, 1959, now abandoned. However, it now hasbeen recognized that acoustic, rather than electric techniques forcomponent strength control have certain advantages.

Therefore, a primary object of this invention is to provide a method ofand apparatus for acoustic-ally eliminating or deemphasizing selectedfrequencies in music emitted by a loud speaker assembly.

This object may be accomplished by mounting two speakers in an enclosureso that the sounds from each are projected through a single opening in awall of the enclosure and so that one of the speakers is spaced fartherfrom the opening than the other speaker by a distance equal to one-halfthe wave length of the frequency to be deemphasized. When the twospeakers are supplied with the same electrical signal, the spacing ofthe speakers results in an acoustical cancellation effect at thefrequency to be deemphasized.

It is convenient to think of a sound wave as a sine curve in which thecrests represent high pressure areas and the troughs represent lowpressure areas. if two waves of the same frequency, but out of phase byonehalf wave length, are added together, the crests of one tends tocancel the troughs of the other. This, of course, is what happens in thepresent invention when the sound waves from the two speakers are broughttogether at the opening in the enclosure wall.

The invention is particularly suited to the deemphasis of high frequencycomponents. In an ordinary speaker system, there will be a large speaker(called a woofer) for producing low frequency tones and a small speaker(called a tweeter) for producing high frequency tones. Since thespeakers for the high frequencies are small, a plurality of them can bemounted conveniently in an enclosure of reasonable size. It is notedalso that the 3,900 c.p.s. range mentioned above usually would beassigned to the tweeter.

In the preferred form of the invention, two identical tweeters aredriven by identical signals. Both are mounted in an enclosure behind anopening in a wall thereof, but they are directed at angles to the axisof the opening and are disposed on opposite sides of the axis.

This arrangement provides not only for the desired cancellation effectdescribed above but also for a dispersion of the high frequency soundsemitted from the speaker enclosure. The latter effect is a particularlydesirable one, in that it substantially reduces the directionalcharacteristic of the speaker assemblies and provides a wider soundcoverage from a single compact enclosure.

A more complete understanding of the invention, and a betterappreciation of its many advantages, will be gained from a considerationof the following detailed description of an embodiment illustrated inthe drawings, in which:

FIG. 1 is a perspective view of the speaker cabinet or enclosure;

FIG. 2 is a perspective view of a twin tweeter mounting connected to therear of the front wall of the cabinet;

FIG. 3 is a plan view of the speaker mounting of FIG. 2 with a part ofthe top wall broken away; and

FIG. 4 is a chart indicating the relative intensities of the variousfrequencies which may occur in the output from the twin tweeterarrangement of the present invention.

The cabinet or enclosure 10 is similar to that disclosed in theco-pending application of Evans and Fowler, Serial No. 854,777, filedNovember 23, 1959, now abandoned.

A large speaker (not shown) for producing low frequency sound componentsis mounted directly behind the large opening 12 in the front wall 11.This may be conventional in construction and it need not be describedhere.

The small opening 13 in the front wall provides an outlet for soundsemanating from a twin tweeter assembly designated generally by thenumeral 16 in FIGS. 2 and 3. This assembly 16 may be secured to thefront wall ill by any suitable means.

The mounting 16 also includes side walls 21 and 22 dispose-d in anangular relationship with respect to the front wall ll of the enclosurein and diverging rearwardly therefrom. An end wall 23 is secured to thewalls l7, l8 and 21 and an end wall 24 is secured to the walls f7, 18and 22. The side wall 21 is longer than the side wall 22 so that the endwall 23 will be spaced rear-wardly of the end wall 24.

A lateral opening 25 in the mounting l6 opposite the speaker as permitsa flow of air from within the cabinet out of the enclosure through themounting, as shown by arrow A in FIG. 3. As explained in the co-pendingapplication of Evans and Fowler identified above, it is desirable thatthe low frequency pressure pulses occurring in the interior of such acabinet or enclosure be allowed to pass to atmosphere along the path ofthe high frequency emissions from the tweeter speaker. This provides apleasing effect by modulating the high frequency tones.

The distances between the front wall 11 of the enclosure is and the twospeakers 19 and 20 are functions of the wave lengths to be deemphasized.The distance from the middle of the wall 23 supporting speaker 19 to apoint in the middle of the opening 13 is greater than the distance fromthe middle of the wall 24 supporting speaker 24) to the same point inthe middle of the opening 13. In order that the sound waves may bedegrees out of phase at the opening 13, the difference in the twodistances should be one-half the wave length of the unwanted frequency.

It is to be understood that this condition does not exist for all soundwaves emitted at this frequency from each speaker. Since sound waves aretransmitted from all sound Waves of this frequency will not intersect atthe point described. Therefore, some sound waves will not have thecomplete cancellation effect described above but there will neverthelessbe some cancellation tendency. It has been proven, in actual practicethat this structural arrangement results in a great improvement of thetone quality of high frequency speakers.

FIG. 4 represents the output from a twin tweeter assembly of the typeshown in FIGS. 2 and 3 set so as to deemphasize frequencies in the rangeof 3,000 c.p.s. This curve is the actual output sound intensityresulting from signals of uniform intensity fed to the tweeters.

Note that frequencies above 3,000 c.p.s. also are affected by the noveldisposition of the twin tweeters of this invention. This is to beexpected. Av difference in spacing numerically equal to one-half thelength of a 3,000 c.=p.s. sound wave would be numerically equal.

to the length of a 'full wave of 6,000 cps. frequency, etc. Thus, someof the higher frequencies will be accentuated and some will bedeemphasized along with the 3,000 c.p.s. sounds. These variations havenot been found, to be unpleasant or to detract from the. desirability ofthe invention. e

The angular relationship of the speakers also provides a larger area ofcoverage of the sound emitted therefrom. The speakers 19 and 20 willproject beams angularly from the enclosure It) in opposite directions.This provides a flaring pattern for the high frequency emissions fromthe enclosure, and permits these tones to be heard clearly at variouspointsin the room.

In view of the many variations and modifications which will suggestthemselves to persons skilled in the art, it is intended that theforegoing description of an illustrated embodiment of the invention beconsidered as exemplary only and that the scope of the invention beascertained from the following claims.

I claim: i

1. In combination with'a loud speaker enclosure having an opening in thefront wall, a loud speaker mounting secured to the front wall of theenclosure and communicating with an opening therein, said mountinghaving parallel top and bottom walls, a pair of side walls diverging'rearwardly from the front wall of said enclosure, an end wall securedto each of said side walls,

a loud speaker secured to each of said end walls, the

length of one of said side walls being such that one'of said speakerswill be spaced from the enclosure opening 4 a distance greater than thatof the other speaker so that the 'differencein the two distances isequal to one-half the wave length of a frequency in the range of 3,000cycles per second. 1

2. In combination with a loud speaker enclosure having a front wall withan opening therein, a tweeter assembly comprisinga mounting secured tothe front wall W of said enclosure, said mounting having parallel topand bottom walls, a pair of side walls diverging rearwardly from saidfront wall, an end wall secured to each side wall, a tweeter attached toeach of said end walls, one of said side walls being longer than theother side wall so as to space the adjacent tweeter a distance from theopening of said enclosure greater than that of the other tweeter, thedifference in said distances being equal to one-half the wvave length ofa predetermined frequency, and said mounting having an opening thereinopposite said one of said side walls.

3. A loud speaker assembly mounting, comprising parallel top and bottomwalls, a pair of diverging side walls, an end wall secured to each sideWalls, said walls forming an enclosure having a rectangular openingopposite saidend Wall s, loud speakers attached to each end wall, theangle of divergence of the Side walls being such that sound wavesemitted from the central portion.

to space the adjacent loud speaker a distance from'said opening greaterthan that of the other loud speaker, the difference in said distancesbeing equal to one-half the wave length of a predetermined frequency,and said mounting having an opening therein opposite said first sidewall.

References Cited in the file of this patent UNITED STATES PATENTS1,808,174 Maxam June 2, 1931 2,172,871 Giannini Sept. 12, 1939 2,872,516Hoffman a Feb. 3, 1959 FOREIGN PATENTS 100,124 Australia Ian. 18, 9371,000,450 Germany Ian. 10, 1937 OTHER REFERENCES Custom SoundInstallation, Radio and Television News, May 1950', pages 3-5.

1. IN COMBINATION WITH A LOUD SPEAKER ENCLOSURE HAVING AN OPENING IN THEFRONT WALL, A LOUD SPEAKER MOUNTING SECURED TO THE FRONT WAL OF THEENCLOSURE AND COMMUNICATING WITH AN OPENING THEREIN, SAID MOUNTINGHAVING PARALLEL TOP AND BOTTOM WALLS, A PAIR OF SIDE WALLS DIVERGINGREARWARDLY FROM THE FRONT WALL OF SAID ENCLOSURE, AN END WALL SECURED TOEACH OF SAID SIDE WALLS, A LOUD SPEAKER SECURED TO EACH OF SAID ENDWALLS, THE LENGTH OF ONE OF SAID SIDE WALLS BEING SUCH THAT ONE OF